Image sensors for scanning document images typically have a row or linear array of photosensors together with suitable supporting circuitry integrated onto a silicon chip. Analogous devices for creating images in response to digital image data, such as LED printbars in xerographic printers, or ink-jet printheads, include a linear array of image creating structures similarly integrated onto a silicon chip. In either case, because of the difficulty in economically designing and fabricating an array comparable in length to the width of an image to be created or recorded, various additional structures must be used. In the scanning context, it is typical to require optical reduction of an original image so the light from the image is reduced to the array of a single chip; in ink-jet printing, a single chip is caused to reciprocate for numerous swaths across an image substrate. However, it would be preferable in many ways to provide a structure, either for recording or image creation, which creates or records a very large image on a one-to-one basis.
In the scanning context, there currently is available on the market a "full-width-array" scanning device, such as shown for example, in U.S. Pat. No. 5,272,113, in which up to 20 individual silicon chips, each with a small linear array of imaging structures thereon, are butted end-to-end to form what is effectively a single page-width array of photosensors. As alluded to in the '113 patent, a practical problem incident to abutting a plurality of chips into a single full-width array involves spacing the chips relative to each other so that the long array of photosensors formed by the plurality of chips is of a substantially even spacing with a minimum of anomalies, particularly between the last photosensor of one chip and the first photosensor of the next. Further complicating the spacing problem is the question of the thermal coefficient of expansion, or TCE, of the chips themselves, and in particular of the chips relative to the member on which the chips are mounted within the apparatus. Such a thermal mismatch could cause undesirable bowing of the assembly, much in the manner of a bimetallic strip. Such mechanical stressing of the relatively brittle silicon chips is likely to damage the chips.
In the context of apparatus for recording or creating very large images such as posters or engineering drawings, which may be up to 50 inches long in a critical dimension, the creation of very long imaging structures out of butted silicon chips becomes highly problematic. The present invention is directed to a structure of a very long linear array of imaging chips (such as comprising photosensors, LEDs, or portions of ink-jet ejectors) in which some of the practical problems are surmounted.